I recorded the stock horn
and the Fiamm El Grande
with my Android phone. (Shoulda used my camcorder.)
Here are the two sound samples as viewed in AVS Audio Editor:
I don't quite understand the dB scale on the right, why it's in negative numbers, but regardless, the difference is about 3 dB, which means the Fiamms sounds
about twice as loud as the stock horn.
I'm new to this board, and I've only got 12 days of experience with my Leaf; but I do know a lot about audio.
Virtually every consumer recording device (phones, camcorders, MP3 recorders, etc.)
have some type of Automatic Gain Control (usually called "AGC" or "Limiter")
which attempts to record any sound at the highest level it can manage without distortion. When you record two different horns with the same device and look at them in a waveform tool, you still have no idea what their relative volume is unless you are able to turn off all of the various AGC-like circuits and software all along the signal path.
If you don't own pro quality recording or video equipment, then the cheapest way I know to get accurate relative sound pressure level measurements is with a hand held meter like this one: http://www.radioshack.com/product/index.jsp?productId=2103667
which is $50 at Radio Shack.
Perhaps the cheapest way to measure the comparison between horns is to put your favorite song on your MP3 player with your favorite ear buds in place and the volume set to a repeatable level, and slowly walk toward the car from a distance while some one else is honking the car's horn. Stop when you can clearly hear the horn above your music and measure your distance from the car. If you aren't considerably farther from the car with one horn compared to another, then they aren't very different in terms of loudness. This may not measure true differences in Sound Pressure Level (dB SPL), but it should give some indication of dB GIA (Getting an Idiot's Attention).
Taking all of that into consideration, the most important measurement of a car horn's loudness is probably just this: Does it sound louder to you?
Oh, the negative dB numbers on the screen are a measurement compared to "full scale" which is the highest waveform peak that can be defined by that particular bit depth. In other words, if the peak of a wave form reads -3 dB, then that peak is 3 dB lower than the maximum possible peak for that file type. Just to confuse things, peaks are measured with an amplitude form of dB, similar to dBV and this is different from power ratios like dB SPL or dBA. An increase of 10 dB SPL represents 10x as much power, 3.16x as much amplitude (e.g.: voltage on a speaker wire or height on a wave form display)
, and is perceived by most people as twice as loud.